24 Castle Street, Lisburn, County Antrim, BT27 4XD

24 Castle Street is a mid-terrace three-bay three-storey rendered townhouse built around 1712–1713. The building is likely one of the first houses erected after the great fire of Lisburn in 1707, as documented in Cathedral Vestry records. According to these historical sources, the building was constructed by the Reverend Joseph Wilkins, Rector of Lisburn Parish, as a sexton's house for use by the church, with work begun on 19 May 1712 and finished on 16 August 1713.

The house is rectangular on plan, facing northwest, with a pitched synthetic slate roof and synthetic ridge tiles. The rendered walling is painted with ruled-and-lined finish. The ground floor features three distinctive rusticated stone arches, a characteristic feature visible in historic photographs of Castle Street. The central and western arches have corresponding piers and impost mouldings. The western arch incorporates a carriage arch with iron gates and an iron shield above, giving access to the cathedral churchyard. This archway contains two Tudor-style timber supports dating to around 1960. The eastern arch forms part of a twentieth-century shopfront with an aluminium-framed full-height display window and glazed door with sidelights.

The windows retain timber sash construction with 3/3 lights to the second floor and 6/6 lights to the first floor. Some retain cylinder glass. The east elevation is abutted by the adjacent building (No. 26). A redbrick chimneystack rises from the rear elevation; the west chimneystack has been removed and the remaining eastern stack abuts an adjacent stack. Cast-iron guttering on iron drive-through brackets sits beneath convex rendered eaves.

A flat-roofed single-storey extension, dating to around 1950, extends from the rear elevation. The rear elevation is three bays over three storeys with 6-pane timber casement windows to the second floor and replacement timber casement windows to the first floor. Access to the upper floors is provided by a steel bridge built over the extension, leading to a hardwood glazed door at the first floor landing.

The building retains many historic features including sliding sash windows and some internal joinery, though the ground floor commercial conversion has resulted in loss of most internal features. The building was recorded in the Griffith's Valuation of 1856–1864 as the residence of John McClure, the postmaster, with dimensions given as 8x8x3 for the house and 3x8x1 for the gateway. The building functioned as a post office from at least 1852, when Mary Burns is listed as postmistress, until around 1876. From 1880 onwards it was occupied by the sexton of Lisburn Cathedral and was shown in valuation records as property of the Select Vestry. By the mid-twentieth century it had become an estate agent's office, and it is now in use as an optometrist's practice, remaining in the ownership of the Select Vestry of Lisburn Cathedral.

The building has group value as part of the historic fabric of Castle Street and forms an important historic component of the townscape, positioned at the northeast corner of the cathedral plot with its distinctive carriage arch providing access to the cathedral rear.